In order to prevent unauthorized entry to a vehicle, modern access authorization systems or access arrangements in vehicles use electronic security systems in which, in order to authenticate a user, data is communicated between a first communications device of the vehicle and a second communications device in the user's mobile identification transmitter, such as a key or key fob. For this purpose, challenge signals with a particular field strength are first sent out at regular time intervals by the first communications device of the vehicle in order to check whether a mobile identification transmitter is in a proximity area around the vehicle. As a mobile identification transmitter approaches the vehicle and can finally receive its challenge signals, it will respond to receiving a challenge signal with a data telegram comprising a characteristic identification code. In the vehicle, checking of the received identification code can then take place and, in the event of a positive, i.e. successful, result, the validity or the authorization of the approaching identification transmitter can be ascertained.
As a special convenience function, today's access authorization systems provide so-called “welcome lighting” functionality whereby, when an authorized mobile identification transmitter has been detected in the above mentioned proximity area around the vehicle, which can encompass a radius of several meters around the vehicle, lighting sources inside the vehicle such as flashing indicators, dipped beam headlights, interior lighting, etc. can be switched on. The welcome lighting can remain on for a particular length of time after detection of the authorized identification transmitter, or also until such time as the authorized identification transmitter moves away from the vehicle again (i.e. is outside the proximity area).
Particularly in the case of so-called “town cars” which are only moved relatively little, but are frequently entered and exited, the problem may arise that, because of the frequent triggering of the welcome lighting, the car battery is progressively discharged over time. In other words, the ratio of battery charging time to battery drain is particularly poor (in favor of battery drain). The only conceivable solution to this problem would be, particularly for town cars, to use larger-sized car batteries which, however, mean both additional weight and unnecessarily large space requirement.